This application claims the benefit of priority under 35 U.S.C. Sec. 119 from German patent application Ser. No. 19722121.1, filed on May 27, 1997.
The invention relates to a device and a method for distinguishing and automatically identifying and classifying tools.
When a workpiece is being processed in machine tools, for example by grinding, the tools, for example the grinding wheels, which are used in the machine tool, are matched to the respective processing step. In addition, the tools are often subject to extremely rapid wear. The frequent changing of the tool which is necessitated by these two factors is alleviated by rapid-change systems which may be equipped with a magnetic tool attaching means (DE 22 61 014 C3, DE 33 42 199 A1).
The machine tool can thus be provided with the correct tool very quickly. However, a numerically controlled machine tool must also xe2x80x9cknowxe2x80x9d which tool it is equipped with and what properties this tool has. For this reason, it has been necessary hitherto to enter manually a tool number and input the tool properties, for example the permitted stepping speed or the wear limit, which is not only relatively time-consuming but also constitutes a considerable source of errors.
In other fields, a very wide variety of automatic identification systems are already in use, for example the widespread bar code labels with the associated bar code readers which operate according to the optical principle, or the transponders which are activated in an inductive, contactless fashion and read out.
However, in the field of machine tools such identification systems have not acquired any practical significance. Opticals systems are generally susceptible to contamination, and the use of transponders, that is to say of complicated and expensive components, makes little sense in wearing parts such as tools. Moreover, the application of such coding aids frequently leads to an unacceptably high unbalance of the rapidly rotating tool. However, for reasons of cost, balancing of the tool is to e avoided.
DE 35 18 902 describes a device for identifying grinding wheels in which the grinding-wheel mounting flange on which the grinding wheel is attached has a code in the form of concentric grooves. A reading device can be applied to the end side of the grinding-wheel mounting flange with the grooves, which reading device comprises a number of mechanical microswitches which are arranged at intervals in the radial direction and which detect the presence or absence, as well as the depth, of the coding grooves.
This arrangement has the disadvantage that the grooves in the mounting flange have to be produced very precisely, which is costly. In addition, the cutting of grooves requires a relatively large volume from which material can be removed. During the manufacture of wearing parts, this leads to unacceptable increases in costs. Also, this system, like optical systems, is sensitive to contaminations.
DE 36 37 128 A1 discloses a device for identifying rotating tools, such as drills, which has the features of the preambles of claims 1 and 9. However, complete evaluation of signals is possible here only if, in addition to the output signals of the reading unit, which contain information relating to the arrangement of the coding elements on the circumference of the tool, additional information is lade available, which defines a reference point on the tool in order to permit an unambiguous identification and classification of the tool. For this purpose, in an exemplary embodiment, an additional rotational-speed actual value signal transmitter is provided which senses the rotational speed of an engine shaft or gearbox shaft in order to drive the tool, so that information relating to the instantaneous position of the tool can be obtained during the procedure of reading the coding elements. This means that, in addition to the reading unit, a further sensor is necessary, whose incremental output signals are also included in the signal processing of the output signals emitted by the sensor of the reading unit.
The invention is based on the object of providing a method and a device which make it possible to identify and classify unambiguously a rotating tool using only a single sensor.
This object is achieved according to the invention with a device according to patent claim 1, and a method according to patent claim 1.
Advantageous refinements of the invention are given in the subclaims.
By determining that coding element which represents the first sensed coding element of a pair of coding elements with the smallest interval, and by determining this coding element as a reference element, i.e. as a zero point for the following count, an unambiguous identification and classification of the tool is possible solely by skilfully evaluating the sensed signals without an additional sensor, such as an incremental rotational-speed sensor being necessary for this.
When the invention is applied in the case of a grinding wheel and a grinding machine, the coding consists, preferably, in a number of drilled holes which are applied to the circumference of the metallic base body of the grinding wheel. The drilled holes are arranged in the circumferential direction with a specific pitch spacing. For this purpose, the 360 degrees of the circumference may, for example, be divided into constant intervals and the presence or nonpresence of a drilled hole at a specific pitch point contains the information in binary form (for example 0=no drilled hole, 1=drilled hole). However, the information can also be expressed as a different distance between the drilled holes or in the number of successive drilled holes and the like. In all cases, a large number of combination possibilities, and thus a high information content, can be obtained with relatively few drilled holes (for example 6) which are distributed with relatively fine pitch spacing over the circumference. The large number of combinations is the result here of the distribution of the small number of drilled holes over the large number of possible pitch spacing positions.
The spindle of a machine tool, which is in any case controlled precisely, provides many possibilities in terms of the fineness and manner of pitch division.
From the large number of possible combinations, those which do not provide any unbalance or provide only a small degree of unbalance of the tool (below a prescribed limit value) can be selected. Even if only the combinations which lead to no imbalance, or only to a negligible degree of unbalance, are selected, the number of remaining possible combinations for coding the tool is still sufficient. If appropriate, the drilled holes can also be provided symmetrically with respect to the axis of rotation, that is to say the information can, for example, be provided on a semicircle and repeated on the second semicircle.
The number of drilled holes is advantageously constant. In this case, reading errors can be detected very easily when the rotational speed is known, because the completion of a full rotation can then be inferred from the passage of a prescribed period of time.
The presence of a drilled hole can, in the simplest case, be determined by means of a fixed, inductive proximity switch, which is attached to the machine tool (or to another machine such as a tool dressing device or a sharpening device) in the vicinity of the grinding wheel. Such proximity switches are very robust components which are of simple design and cheap. The reading procedure takes place while the tool is rotating and the drilled holes are moving past a proximity switch. The information is read off from the tool at the latest after one complete rotation of the tool. This reading off is carried out preferably during one relatively slow rotation of the tool before the work on the machine begins.
Instead of drilled holes, cams, grooves and inserts made of a non-ferromagnetic material on the circumference of the tool can also be sensed by the inductive proximity switch.
Instead of the inductive proximity switch, other sensors which operate optically, electrically or magnetically or electro-optically, etc. may be used as the reading unit. The reading unit merely has to be capable of sensing successively the markings on the tool as the tool moves past.
The distinguishing system according to the invention is advantageous particularly in the case of tools and machine tools with a rapid-change system, possibly with a magnetic mount, since the type of tool no longer has to be input manually into the machine. As a result, not only is the process of changing the tool speeded up but inputting errors are also avoided.
Overall, the device according to the invention is very simple in terms of production technology. No relatively large modifications are necessary of the tool and the reading unit is small and robust and can be attached to the machine tool without relatively large expenditure.